1. Field of the Invention
The present invention relates to a method for producing a semiconductor device and a semiconductor device produced by that method. More particularly, it relates to a method for producing a semiconductor device having a single crystalline substrate consisting of a III.sub.b -V.sub.b group compound, and the semiconductor device produced thereby.
2. Description of the Related Art
Since in a single crystalline substrate of a III.sub.b -V.sub.b group composition such as GaAs, Ga.sub.1-x In.sub.x As (0.001.ltoreq.x.ltoreq.0.01), InP, etc., the electron mobility is large, it is used for a production of field effect transistors (FET's) used in a high frequency zone, analog IC's, and high speed digital IC's, among others. The III.sub.b -V.sub.b group compound is hereinafter referred to as the III-V composition.
The semiconductor device is produced by the steps of, preparing a single crystalline substrate having a III-V composition, implanting conductive impurities into the substrate, and annealing the implanted substrate to activate the same. This method is well known as an ion implanting process having a higher productivity than other processes, such as an epitaxial growth process.
In the ion implanting process for producing such a semiconductor device, a semi insulating substrate having a specific resistivity of 1.times.10.sup.7 .OMEGA..multidot.cm or more is used, as this ensures that each IC component element can be easily electrically isolated.
However, in a conventional semiconductor device produced by using the semi insulating substrate such as GaAs or Ga.sub.1-x In.sub.x As, when the semi-insulating is annealed after ion implantation, the specific resistivity of the substrate is decreased with the result that the isolation of the component elements becomes unsatisfactory, and further, after the ion implantation, the ion activity in one substrate or further substrates becomes nonuniform. Therefore, the production yield of these semiconductor devices is lowered.
The annealing process in the above-mentioned ion implanting process for producing a semiconductor process is carried out by a process using a known resistivity heating furnace insulated by rock wool, etc., and a lamp annealing process using an infrared ray lamp wherein a substrate is irradiated with rays having an incoherent property, to heat the surface of the substrate.
In the conventional annealing process, heat conditions are well known but the effects of the cooling after the annealing were unknown. Namely, after the annealing, the specific resistivity of non-ion-implanted portions is not sufficiently improved, with the result that the specific resistivity becomes less than an aimed 1.times.10.sup.7 .OMEGA..multidot.cm, and thus the electrical isolation between each component element of IC becomes unsatisfactory.